The present invention relates to battery systems. In particular, the invention relates to a battery architecture, construction or arrangement which provides thermal management of the battery.
Batteries are utilized in such applications as electric vehicles, industrial systems, computers, as well as countless other applications. Particular applications, such as an electric car which is powered by a battery, require that the battery provide a large amount of energy and power and minimal weight and volume. For example, a battery in an electric car must be capable of providing a sufficient driving range and sufficient power for the vehicle to have acceptable driving performance. Further, these applications often also require that the battery be contained in small light packages. These packaging, power, and energy requirements often lead to heat dissipation problems.
Particularly, a large amount of heat is produced by the chemical reactions and the circuit paths which provide the power and energy needed to operate an electric vehicle. This phenomenon is partially the result of I.sup.2 R heating in the battery. Thus, batteries should be thermally managed by cooling or dissipating heat to avoid battery malfunction.
Further, battery performance and battery life are temperature dependent. Batteries perform optimally in particular temperature windows. Thus, batteries may have to be heated or cooled to obtain optimum battery performance and long battery life. For instance, a battery may have to be thermally managed by heating to operate the battery in an optimum temperature range.
The construction of prior art battery systems is not adapted for proper thermal management. Generally, batteries are comprised of smaller individual battery cells or modules. Each cell or module is encapsulated in a plastic or other insulative material. These cells or modules are also all contained in a main plastic or insulative material. Thus, heat which is generated in the individual cells must pass through the individual cell walls and the main battery containment, both of which often are poor thermal conductors.
Heretofore, batteries or battery systems have been cooled by fans, cooling coils, or arrangements employing spaces between individual battery cells. These systems have been found to be uneconomical or ineffective for applications in which the battery generates large amounts of heat. Further, these systems often utilize moving parts or hazardous materials in the thermal management systems thereby undermining reliability.
U.S. Pat. No. 1,152,247, issued to Walker on Aug. 31, 1915, discloses a battery which utilizes a corrugated metal jar. An inner jar of suitable nonconducting material for housing electrochemical components is placed within the outer metal jar. Air passages within the corrugated sides of the metal jar provide a means for cooling the battery system within the inner jar.
U.S. Pat. No. 4,007,315, issued to Brinkmann et al. on Feb. 8, 1977, discloses a multi-cell battery cooling system utilizing cooling elements immersed in the electrolyte. The cooling elements are connected in series or in parallel to the individual cells. The cooling elements have high heat conductivity and electric resistance. This system is disadvantageous as it requires a cooling system and cooling elements to cool the battery effectively.
U.S. Pat. No. 3,834,945, issued to Jenson on Sep. 10, 1974, shows a water cooled industrial battery. The water cooled industrial battery includes intercell connectors with a water passage molded into the intercell connectors. Water is caused to flow through the passage for thermally managing the battery. The cells of the battery are arranged in a four by six matrix with all intercell connectors on one side of the battery.
Thermal management systems for batteries are constrained by various design criteria. Particularly, a thermal management system should be: 1. simple and reliable; 2. of minimal volume; 3. of minimal weight; 4. compatible with the environment of the application and battery; 5. of minimal impact on energy per unit mass, energy per unit volume, power per unit mass, and power per unit volume; and 6. of minimal cost. These six design ideals for a thermal management system may be approached by utilizing an arrangement which advantageously provides a heat conductive path from the inside of the battery to the outside of the battery. Further, an ideal thermal management system utilizes existing battery components to provide the heat conductive path.